1. Field of the Invention
The present invention relates generally to a memory mounting judgment circuit. More specifically, the invention relates to a circuit which makes judgment whether ROM (Read Only Memory) is mounted or not.
2. Description of the Related Art
In general, programmable device or CPU (Central Processing Unit) having a boot function perform predetermined operation with reading out a content stored in ROM upon power-ON reset. Accordingly, in a computer system employing such device or CPU, the system cannot be correctly started up unless ROM is mounted. Therefore, it becomes necessary to automatically check whether ROM is mounted and to mount ROM if not mounted.
A technology for checking whether a parts to be mounted is mounted or not, has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. Heisei 3-113543. Discussion for the prior art will be given with reference to FIGS. 11 and 12.
As shown in FIG. 11, in the prior art disclosed in the above-identified publication, mounting of ROM is checked by employing an optical sensor. Namely, in the condition where ROM 202 is mounted, a light beam emitted from a light emitting device 201 is reflected at the bottom portion of ROM 202. When the reflected light is received, a photosensing element 203 turns ON. In response to turning ON of the photosensing element 203, an output of a comparator 204 becomes HIGH level.
On the other hand, in the condition where ROM 202 is not mounted, the photosensing element 203 may not receive the light from the light emitting device 201. Therefore, the photosensing element 203 is held OFF to make the output of the comparator LOW level. Thus, by means of the optical sensor, check can be performed whether ROM is mounted or not. It should be noted that ROM is mounted in a socket 205 as shown in FIG. 12. And, the light emitting device 201 and the photosensing element 203 are located at the mounted position of the socket 205.
On the other hand, Japanese Unexamined Patent Publication No. Heisei 1-303692 discloses another prior art. The prior art disclosed in this publication will be discussed with reference to FIGS. 13 and 14. In this prior art, as shown in FIG. 13, check is performed whether an IC card 212 is mounted or not by means of a microswitch 211. Namely, when the IC card 212 is not mounted, the microswitch 211 is held OFF, and when the IC card 212 is mounted, the microswitch 211 turns ON. Accordingly, depending upon ON and OFF of the microswitch 211, whether the IC card 212 is mounted or not can be checked.
On the other hand, in the prior art illustrated in FIG. 14, whether the IC card 212 is mounted or not is detected depending upon whether a signal line 222 which is fixed at low level is connected to a RESET signal line 221 which is pulled up to a predetermined level by a pull-up resistor 223. Namely, when the objective device is not mounted, the RESET signal line 221 becomes HIGH level due to presence of the pull-up register 223, and when the IC card 212 is mounted, the RESET signal line 221 is grounded and thus becomes LOW level. Accordingly, whether the IC card 212 is mounted or not can be checked.
In the prior art shown in FIGS. 11 and 12, set forth above, since the optical sensor has to be arranged right below ROM. In certain shape or size of the ROM socket, the optical sensor may not be arranged at the desired position. Also, since a reflected light of the light emitted from the light emitting device, a certain distance between the light emitting elements and ROM is inherently required. However, in certain kind of socket, the distance becomes zero to make it impossible to receive the reflected light.
On the other hand, in case of the method employing the microswitch as shown in FIG. 13, when it is applied for checking whether ROM is mounted or not, the microswitch has to be located at a position to be turned ON and OFF depending upon presence and absence of ROM to be mounted. This can be significant constraint in mounting. Therefore, such prior art can be impossible to practice in viewpoint of arrangement.
On the other hand, in case of the prior art shown in FIGS. 11 and 12, a space above ROM has to be empty so that the light should not be reflected when ROM is not mounted. If substrate, casing or so forth is present immediately above ROM, erroneous detection of mounting of ROM can be caused by the light reflected by these element. For necessity of providing an empty space above ROM, mounting density can not be increased.
On the other hand, considering the case where the prior art shown in FIG. 14 is employed in checking whether ROM is mounted or not. It becomes necessary to have a pin or pins fixed at low level or pins fixed at high level among pins of ROM. However, a little number of ROMs having the pin or pins fixed at low or high level are available in the market. Accordingly, when checking of mounting of ROM is to be realized by this method, there is no method other than preparation of custom-made ROM. Thus, ROMs available in the market cannot be used freely.
Furthermore, in the prior art shown in FIGS. 11 and 12 set forth above, it is possible to damage the sensor during repeating of mounting and unmounting of ROM. Namely, it is frequently performed to unmount ROMs using principle of leverage by inserting a tool, such as a driver, tweezers or so forth between ROM and the socket upon removal of ROM, in general. In such case, the sensor can be damaged by the tip end of the driver or so forth when the sensor is provided below ROM.
Accordingly, in the prior art set forth above, improvement of reliability in detection of presence or absence of ROM, increasing of package density can be prevented. In the alternative, a problem can be encountered in arrangement.